Dual rate jack system for lift trucks

ABSTRACT

A JACKING SYSTEM FOR LIFT TRUCKS AND THE LIKE WHICH EMPLOYS A ROLLING DIAPHRAGM AND A PISTON UNIT TO ACHIEVE A DUAL JACKING RATE, A FAST RATE IN AN UNLOADED CONDITION AND A SLOWER RATE, WITH INCREASED MECHANICAL ADVANTAGE, FOR LOADED CONDITIONS ON THE JACKING SYSTEM.

March 1971 s. M. BRASSINGTON 3,567,240

DUAL RATE JACK SYSTEM FOR LIFT TRUCKS Filed April 11, 1969 I 2 Sheets-Sheet 1 March 2, 1971 s. M. BRASSINGTON DUAL RATE JACK SYSTEM FOR LIFT TRUCKS 2 Sheets-Sheet 2 Filed April 11, 1969 FIG. 6

FIG. 4

INVENTOR:

SAMUEL M. BRAS SINGTON BY:

,:Z HIS ATTONEYS United States Patent Olific 3,567,240 DUAL RATE JACK SYSTEM FOR LIFT TRUCKS Samuel M. Brassington, 1101 Kenwal Road, Concord, Calif. 94521 Filed Apr. 11, 1969, Ser. No. 815,460 lint. Cl. 1566f 9/06 US. Cl. 280-4112 Claims ABSTRACT OF THE DISCLOSURE A jacking system for lift trucks and the like which employs a rolling diaphragm and a piston unit to achieve a dual jacking rate, a fast rate in an unloaded condition and a slower rate, with increased mechanical advantage, for loaded conditions on the jacking system.

BACKGROUND OF THE INVENTION In hand lift trucks used for moving loaded pallets, an integral hydraulic jack is usually employed to lift the load onto the truck so that it is supported on the wheel carriages of the truck. conventionally, the lift forks of the truck are positioned in a lowered or retracted position so that they can be maneuvered under the pallet and thereafter the jack is extended to lift the forks under the loaded pallet so it will be supported on the wheel carriages of the truck. Often the hydraulic jack in a hand lift truck is manually operated and, since considerable force is required to lift a loaded pallet, the working area of the piston of the pump in the jack system is considerably smaller than the area of the lift piston in the hydraulic jack in order to obtain the necessary mechanical advantage. As a result of this relationship, the lift truck raises the same increment in height for each stroke of the pump whether the truck is in a loaded or unloaded condition.

Thus, when an operator places a hand lift truck or similar device under a pallet, he is often required to expend considerable time and effort to bring the lifting structure (forks) of the truck into engagement with the loaded pallet from a lowered or retracted position. While the greater mechanical advantage is needed for lifting a load, it is this relationship that requires the operator to expend considerable time and effort to bring the lift truck into contact with the pallet prior to the time the high mechanical advantage is necessary. Thus, both time and effort can be saved if the jacking rate in the unloaded condition can be increased by sacrificing some of the mechanical advantage for increased speed and thereafter automatically decreased to regain the necessary mechanical advantage as the jacks assume the load of the pallet. For example, if an unloaded hand lift truck had a system with a jacking rate in the unloaded condition which is four times that of the jacking rate in the loaded condition, the operator could move the lifting structure (forks) into engagement with the load with one quarter the number of pump strokes required in a conventional system.

While a dual rate jacking system is desirable in such lift trucks, it often is not practical because excessive costs tend to offset the values obtained in saving operator time and effort. Since a dual rate jacking system for a lift truck, such as described above, would normally be complex and require a large number of components, fitted parts, seals, bushings and the like, its costs are considerable. In fact, even in jacking systems for hand lift trucks having the conventional single jacking rate, the cost of this component tends to represent one of the more expensive components of the lift truck. If such a jack system was modified for dual rate action, it is unlikely it could be accomplished cheaply enough to be of substantial value to a purchaser of such a hand lift truck.

3,5672% Patented Mar. 2, 1971 Thus, one object of the current invention is to provide an inexpensive dual jacking rate unit for lift trucks and the like which is less costly than many single rate jacking systems now found in such trucks.

It is also an object to provide a unitized jacking system which can be replaced as a component nearly as cheaply as most conventional jacking systems can be repaired.

Further, many additional advantages and objects of the instant invention will be apparent from the following description.

SUMMARY OF THE INVENTION A dual rate jacking system for lift trucks and the like according to this invention includes an inner lift piston reciprocally mounted in an inner chamber, an outer lift piston integrally formed with said inner lift piston so it is concentric therewith reciprocally mounted in a separate outer chamber concentric with said inner chamber, a source of pressurized fluid connected to said inner chamher, a passage between said inner chamber and said outer chamber having a pressure relief check valve and a oneway siphon in communication with a supply of fluid and said outer chamber whereby said outer chamber will fill with fluid as the pistons rise even though said pressure relief check valve is closed.

A fluid release valve having controlled fluid communication with both the inner and outer chambers is employed to vent both of these chambers simultaneously to lower the dual rate jacking system.

Costs are greatly reduced by employing a rolling diaphragm in the construction of the outer lift piston structure to avoid the necessity for multiple machinery of components, use of the concentric design improves compactness and with the rolling diaphragm can, when incorporated in a lift truck, greatly improve efiiciency by providing a dual rate feature.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be better understood by referring to the attached drawings in connection with the description thereof wherein:

FIG. 1 is a perspective of a hand hydraulic lift truck incorporating the novel dual rate jacking lift system;

FIG. 2. is a perspective with parts broken away of a dual rate jack lift system portion of the truck illustrating greater detail;

FIG. 3 is a vertical section through the novel dual rate jack lift system;

FIG. 4, a section of the wall structure, illustrates how the rolling diaphragms can be secured within the novel lift system;

FIG. 5 is a perspective of a valve cock for lowering or retracting the novel jack lift system; and

FIG, 6 is a broken away section of the pressure release valve in which the valve cock is received.

BRIEF DESCRIPTION OF A PREFERRED EMBODIMENT Referring to FIG. 1, a hand hydraulic lift truck 10 is shown which has a frame or bogie 11 supported in a. three point wheel suspension system. The frame or bogie includes two pallet forks 12 and a forward arch structure 13 and linkages, which when operated through the action of the asociated hydraulic jacking system 14 raises and lowers the frame of the bogie in a level manner on its three point wheel suspension system.

A bogies wheel 15 is connected at the outboard end of each fork 12 through a lever attachment 16 which is centrally pivoted with a pin 17 on the end of its associated fork end. Each bogie wheel is mounted at one end of its lever attachment and the opposite end of the lever attachment is connected to a bar linkage 18 extending in a channel on the under side of each fork to a bell crank structure 19 journalled in the arch structure 13 in the forward portion of the frame or bogie.

Axial reciprocation of each bar linkage will articulate its lever attachment and cause its associated bogie wheel 15 to swing about its pivoted connection in the fork end causing the associated end of the fork to raise or lower as the bogie wheel extends or retracts.

The bell cranks of the structure 19 are duplicated on both sides of the arch structure so that each bar linkage 18 is connected to an end of a separate arm 19a of a crank while the spaced-apart other arms 19b of the bell cranks are joined on opposite sides by pivots 20, on a horizontal thrust plate 21 on which a steering plate 22 is swingably supported. A vertical axle post 23 is joined to the bottom of the steering plate and projects through a central aperture in the thrust plate for supporting the forward wheels of the truck. The axle post includes a horizontal bore 24 through which a horizontal axle is received for supporting a pair of dirigible wheels 25, one of which is mounted on each side of the post to complete the three point wheel suspension. A handle 26 for manipulating the lift truck is pivoted on spaced apart ears 27 with pin 28 on the steering plate and when the handle is folded forward, it can move in a sideways manner to turn the axial support post, thereby steering the pair of dirigible wheels which are journalled in the axle post, for maneuvering the truck.

Located on the top of the steering plate 22 is the hydraulic jacking system 14 which is attached to the plate with bolts 29 and extends from the thrust plate to a thrust bearing (not shown) located in the crown 30 of the arch structure which allows the jacking structure to pivot with the steering plate when the bogie is loaded and the handle is moved in a sideways manner for steering the truck. Raising or retracting the jacking system through the arrangement described, raises or lowers the frame or bogie of the lift truck in a level manner.

It can be appreciated with the jacking system in a retracted position with the bogie or frame at its lowest vertical ground clearance, the forks 12 can be inserted under a conventional pallet. Thereafter, the jacking system is extended so that the bogie will be elevated on its three point wheel suspension, bogie wheels 15 and dirigible wheel 25, thereby lifting the pallet and any load thereon for transport,

Normally, the foregoing described lift truck is somewhat conventional, except for reference to the dual rate jacking system which has been indicated as being incorporated in the instant lift truck, in place of its conventional single rate jacking system.

Generally, this jacking system 14 includes a lift or jack in a pump 41 which is preferably integrally attached to the jack with bolts on its cylindrical enclosed base portion 43 which serves as a hydraulic fluid reservoir 43a. As previously mentioned, the jack system is attached to the steering plate 22 with bolts 29 and is oriented so that handle 26 is adjacent to the pump, as illustrated in FIG. 2. With this relative arrangement, a yoke 44 composed of two spaced apart straps 45 and a cross head 46 attached with a bolt to the top of the pump rod 47 connect the pump rod on opposite sides of the pump housing 48 to the handle with pins 49 adjacent to lugs 27 on which the handle is pivoted. As a result of this attachment between the pump rod and the handle, as the handle is pivoted fore and aft about its pivoted connection, it will cause the rod to reciprocate in the pump.

As can be seen in FIG. 3, reciprocation of the pump rod 47 in housing 48 will cause piston 49 to reciprocate in its cylindrical chamber 50 within the pump housing. This chamber is connected to the fluid reservoir 43a through an inlet ball check 51 and a high pressure line 52 leads pressurized fluid away from the outlet ball check valve 53, also in communication with chamber 50. Thus,

4 as the piston is reciprocated, it will affect a pumping action, drawing fluid in from the reservoir through the inlet ball check and discharging high pressure fluid through the outlet ball check valve into the high pressure line.

To reduce the cost of the pump construction, piston 49 is not fitted to the wall chamber 50 and only the bore 48a in which rod 47 is received includes a fitted, nonsealed bearing surface. Instead of a fitted piston/cylinder, a rolling diaphragm 54 is connected to the end of the piston with a plate 55 and bolt 56 with the peripheral skirt of the diaphragm secured at the mid-portion of chamber 50 with the retaining ring 57. A removable plug 58 at the bottom of the pump housing facilitates the assembly of the pump and internal attachment of the rolling diaphragm, previously described.

Use of a rolling diaphragm, which is a commercially available part, greatly reduces the cost of the pump and it should be appreciated that the pump itself could be oriented differently relative to the jack 40 and handle 26 so that a different linkage connection between the handle and the pump rod might be employed if this is desirable. The yoke connection illustrated was chosen for simplicity and is not intended to restrict the invention to this type of arrangement,

Referring to FIG. 3, it can be seen the lift or jack 40 is quite unconventional. The cylindrical enclosed base 43 of the jack attached to the steering plate, has concentrically disposed therein a jack post 60 which extends through this disc-shaped element projecting above and below it. The jack post is welded to the base where it projects through the top 61 and bottom 62 to provide in tegral vertical support to the base. The closed bottom end 63 of the jack post is received in a blind bore 31 in the steering post 23 when the unit is mounted on a steering plate, as illustrated.

Inside the jack post 60 is an inner lift piston 64 which is received in the machined bore 65 of the hollow jack post and which includes an O-ring 66 in a central circumferential groove that forms a seal between the lower end of the lift piston and this bore. Actually, the bore of the jack post and the lift pistons outer surface are some of the few closely machined parts in the jack 40.

The high pressure line 52 is connected to a fitting 67 in the jack post and which leads high pressure to the inside of this post below the O-ring 66 on the lift piston. The lower portion 68 of the lift piston includes a series of longitudinal grooves 69 on its exterior surface which allows the high pressure oil from the high pressure line to enter along the wall of the jack post to raise the lift piston. Thus, as the pump is reciprocated (all the drain passages being closed), the lift piston in the bore of the jack post will be hydraulically lifted.

Again referring to FIG. 3, as long as the lift check valve 70 at the bottom of the lift piston remains closed, the movement of the lift piston will be directly proportional to the ratio of its area to that of the area of the pump piston 49. This represents the fast, unloaded jacking rate of the jacking system. However, once the load is engaged by the lifting structures of the truck, the force required will increase and the pressures acting on the bottom of the lift piston will exceed the value set by the spring in the lift check valve sO that fluid will by-pass this valve into its hollow central channel 71 thereby automatically changing the jacking system to a slower rate, with increased mechanical advantage, by the structures described below.

Referring to FIG. 3, integrally formed at the top of the lift piston 64 is a cap structure with two downwardly projecting skirt portions, an inner skirt 81 and an outer skirt 82, which are located near the outer periphery of the cap and are concentric with the lift piston. The top of the cap includes an external recess 83 which receives the thrust bearings in the crown 30 of the forward arch structure 13 of the bogie or frame 11. The inner skirt which is spaced inwardly from the outer skirt and which depends downwardly from the periphery of the cap, includes a threaded internal surface which receives a locking ring 84 for clamping the bead of the inner aperture of a rolling diaphragm 85 about the bottom or mouth of the inner skirt or sleeve, as can be seen in the drawings.

Joined to the horizontal top 61 of the cylindrical base 43 is an upwardly projecting cylinder 86 which is also concentric with the jack post and has a diameter that allows it to fit between the spaced apart downwardly projecting skirts of cap 80 as illustrated. This upwardly projecting cylinder is threadedly joined in its central portion and includes a recess 87 (see FIG. 4) which receives the outer circumferential bead of the rolling diaphragm 85 for retaining it in the wall structure formed by this cylinder.

As a result of the connection of the rolling diaphragm between the skirt and the cylinder described above, the underside of the cap, the inner skirt and the cylinder form a secondary chamber 88 in the jack system which increases the effective lift area or working area of the jack.

For example, if the lift piston has a diameter of 2 inches and the internal diameter of the upwardly projecting cylinder is 6 inches, force would be increased by a factor of 8 when the lift check valve opens with only a slight increase in pressure. Thus, assuming that the lift check valve opens at 200 lbs. pressure, the lift piston below 200 lbs. would rise 8 times faster than it would after the pressure exceeds the value set by the spring in the lift check valve. Further, above 200 lbs. pressure, the mechanical advantage will also increase by a factor of 8. Thus, if 600 lbs. was generated by the lift piston in the unloaded condition, 4800 lbs. of force would be available after the check valve opened with a slight increase in pressure in the system. This increased mechanical advantage will result from fluid entering the secondary chamber 88 via the lift check valve 70, passage 71 and ports 90 leading from the passage to the secondary chamber 88.

In such a dual rate system, it would be of no utility if chamber 88 had to be pumped full of hydraulic fluid in order to achieve the additional mechanical advantage once the pressure under the lift piston had exceeded the value set by the spring tension of the lift ball check valve. Thus, as the lift piston rises at a fast rate, i.e., low mechanical advantage, a siphon 91 extending into reservoir 43a and having a one-way check 92 connects the reservoir and chamber 88 which allows the latter to fill with hydraulic fluid as the lift piston rises at a pressure below those which will unseat the lift ball check valve. Thus, when the fluid pressure under the lift piston becomes sufficient to by-pass t the lift check valve, chamber 88 will be full of hydraulic fluid and any fluid passing the lift check valve will be communicated at chamber 88 for an increased mechanical advantage and an immediate lifting action.

Once the loaded pallet has been lifted onto the wheel carriages of the truck and transported it is necessary to lower the jacking system 14 in order to drop the forks of the lift truck from the underside of the pallet so that the truck can be removed. This is accomplished with a release valve 100 which includes a valve cock 101 having a groove 102 at each end for sealing it in the bore 103 of the valve. The valve is located adjacent to the jack post 60 close to the underside of the upper horizontal plate 61 of the cylindrical base structure 43. In this location, a passage 105 communicates with the fluid operating on the lift piston and passage 106 communicates with the secondary chamber 88 which provides the increased mechanical advantage, once the hydraulic fluid passes the lift check valve. Thus, when the valve cock is turned so that passages 105 and 106 are communicated directly to the reservoir through passage 107 of the valve, fluid will be drained from both chambers and the jacking system will retract. This will lower the bogie 11 on the wheel carriages of the truck for removal from under the pallet. FIG. shows the valve cock and FIG. 6

is the cross-section of the release valve showing the relative relationship of the previously described components.

As can be seen in FIG. 2, a foot trip lever 110 is attached with screw 111 to the end of the valve cock 101 and the lever is loaded with spring 112 so that the pedal is maintained against a stop 113. Depressing the foot pedal will cause the valve cock to rotate and communicate passages 105 and 106 to reservoir through passage 107 thereby allowing the jack system to retract. A filler plug 114 with a breather filter 115 therein prevents vacuum or pressure build-up in the reservoir during operation of the jack.

The above described embodiment of the invention is not intended to be limiting and is representative of a structure in which the novel concept of the instant invention can be employed.

If desired a small check valve can be incorporated in port 107 of the release valve to prevent drainage of the secondary chamber when the valve is turned to vent the fluid back to the reservoir 43a.

I claim:

1. A dual rate jacking unit for lift trucks and the like comprising:

an inner lift piston reciprocally mounted in an inner lift chamber;

an outer lift piston integrally joined with the upper portion of said inner lift piston so it is concentric therewith, said outer lift piston reciprocally associated with an outer lift chamber concentric with said inner lift chamber;

a source of pressurized fluid connected to said inner lift chamber;

a passage between said inner lift chamber and said outer lift chamber having a pressure opening check valve means allowing fluid to enter said outer lift chamber from said inner lift chamber above a preselected pressure level; and

one-way siphon means connected between said outer lift chamber and a supply of fluid thereby allowing said outer lift chamber to fill with fluid at pressures below those operable to open said pressure opening check valve when the pistons extend.

2. The dual rate jacking unit as defined in claim 1 wherein the outer lift piston includes telescoping cylindrical parts with said parts connected with a rolling diaphragm member.

3. The dual rate jacking unit as defined in claim 1 wherein a fluid release valve means is connected to both the inner lift chamber and the outer lift chamber and is operable to simultaneously vent fluid from said chambers.

4. The dual rate jacking unit as defined in claim 3 wherein the source of pressurized fluid is a fluid pump.

5. The dual rate jacking unit as defined in claim 4 in combination with a hand lift truck and linkage con nected between the pump and the handle of said lift truck whereby fore and aft movement of said handle will cause reciprocation of said pump.

6. A dual rate jacking unit for lift trucks and the like in combination with a pump comprising:

a support member;

a hollow jack post mounted in said support member said jack post having fluid communication with said P p;

a lift position reciprocally mounted in said jack post, said lift pistion having a central passage therein;

check valve means between said central passage and said jack post whereby fluid will not enter said passage below a preselected pressure;

a cap structure connected to the upper portion of said lift piston, said cap structure having at least one downwardly depending skirt concentric with said lift piston;

7 an upwardly extending sleeve concentric to said lift piston mounted on said support structure to telescope with said skirt of said cap structure; rolling diaphragm means connected between said sleeve and said skirt whereby a secondary chamber is formed;

port means connecting said central passage in said lift piston to said secondary chamber; and

a one-way siphon means connected between said secondary chamber and a fluid reservoir whereby fluid above preselected pressure of said check valve means will afford increased mechanical advantage by acting on the added surface area provided by said secondary chamber.

7. The dual rate jacking unit defined in claim 6 wherein a fluid release valve means is connected to the jack post and the secondary chamber to simultaneously vent the fluid therein when actuated.

8. The dual rate jacking unit defined in claim 7 wherein the support member includes a fluid reservoir which serves as the fluid supply for the pump and the one-way siphon means.

9. The dual rate jacking unit defined in claim 6 wherein the unit is mounted on a hand lift truck and the pump is reciprocated by linkages connected between it and the handle of the lift truck to raise and lower the truck.

10. The dual rate jacking unit defined in claim 9 wherein the pump is mounted on the support member.

References Cited UNITED STATES PATENTS LEO FRIAGLIA, Primary Examiner L. J. PAPERNER, Assistant Examiner US Cl. X.R. 

